Fixed: DatabaseConnection_mysql::$utf8mb4Supported is never initialized.

[kiamlaluno]

DatabaseConnection_mysql::utf8mb4IsSupported() uses a property ($utf8mb4Supported) to avoid running the CREATE TABLE {backdrop_utf8mb4_test} (id VARCHAR(255), PRIMARY KEY(id(255))) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci ROW_FORMAT=DYNAMIC ENGINE=INNODB query more than once, but that property is never initialized (and the query will be always executed when DatabaseConnection_mysql::utf8mb4IsSupported() is called).

DatabaseConnection_mysql::utf8mb4IsSupported() must be changed to set that property to FALSE (when an exception is caught) or TRUE.

[herbdool]

This makes sense to me.

[quicksketch]

Nice catch on this oversight @kiamlaluno! I don't know how many times this method gets called within a single request, but it's clear that the intention was to set the property only once per request.

I merged backdrop/backdrop#4637 into 1.x and 1.27.x. Thanks @kiamlaluno and @herbdool!